In a manner known in itself, a navigation solution is determined by a mobile receptor from electromagnetic signals emitted by satellites of one or several satellite global positioning systems. Such a satellite, also called constellation, is known under the acronym GNSS (Global Navigation Satellite System”).
There are currently several GNSS systems, which in particular include the GPS system, the GLONASS system and the GALILEO system.
Each navigation system generally comprises the geographical position of the mobile receptor, its speed and the time synchronized with the corresponding GNSS system.
In the context of applications using navigation systems for sensitive operations, for example aeronautic or maritime navigation, it is necessary to associate each determined navigation solution with a protection level characterizing the reliability of this navigation system.
Such a protection level is in particular determined from the likelihood of provision of a navigation solution whose error rate does not exceed a stated integrity threshold (also known as “Hazardous Misleading Information”) and the likelihood of false alarm.
This protection level is further determined using redundant information relative to the corresponding navigation solution. This redundant information is in particular determined from electromagnetic signals emitted by satellites visible by the receptor when the number of these satellites exceeds the number of satellites necessary to determine a single navigation solution.
Different methods of making it possible to determine protection levels associated with the provided navigation solutions are already known in the state of the art.
Among these methods, the RAIM (Receiver Autonomous Integrity Monitoring) method makes it possible to determine protection levels from redundant information obtained from satellites visible from a single constellation based on the likelihood of fault of each of the satellites in this constellation.
An improved version of this method, called ARAIM (Advanced Receiver Autonomous Integrity Monitoring) is also known, which makes it possible to determine protection levels from redundant information obtained from satellites visible from several constellations. Relative to the RAIM method, this improved version allows greater availability of aeronautic receptors, in particular in approach phases.
To that end, the improved version takes account not only of the likelihoods of simple faults of the satellites of each constellation, but also the likelihoods of faults affecting several satellites at once. In order to determine the corresponding protection levels, this method uses an integrity relationship linking the likelihoods of providing an erroneous navigation solution and of raising a false alarm at the corresponding protection.
However, given that the integrity relationship has no analytical solution and includes mathematical functions that are costly to bring numerically together, the implementation of this improved method requires large computation capacities from the receptor. Indeed, to determine the protection levels in real time, it is necessary to numerically resolve the integrity relationship for each of the provided navigation solutions. This then makes it difficult, or even impossible in real time, to implement this method in receptors having limited computing capacities.